In an admittedly unscientific but telling telephone survey, Ken Jacobs, chairman of the Center for Labor Research and Education at UC Berkeley, asked 21 union leaders representing 315,000 workers in California this summer whether health care would be a central issue in their contract negotiations. All 21 said it would.

"That is not a shock," Jacobs said, because runaway increases in health insurance costs have been the dominating theme in collective bargaining in recent years. The thorny issue is not going away. Asked Jacobs: "Who is going to pay for it?"

Employer-sponsored health insurance has protected Americans since the end of World War II. But much is changing.

In a study set for release today, Jacobs cites federal data that show the proportion of workers covered by employer-sponsored health coverage has fallen by almost five percentage points in both the United States and California since 2001. Between 2004 and 2005, it dropped 2.3 percentage points in the state.

Many experts argue that the problem cannot be resolved at the bargaining table. Making sure that workers have health coverage will have to be resolved through public policy.

In San Francisco, labor-supported legislation pushed by Supervisor Tom Ammiano and Mayor Gavin Newsom would provide health insurance to about 82,000 uninsured residents beginning next year. The program would be funded through contributions from taxpayers, local businesses and individual premiums. Newsom has cited it as an example of political will to try to resolve an intractable problem.

Restaurateurs and other small- business owners, who say it will push them out of business, are expected to mount a legal challenge. San Francisco Chamber of Commerce Vice President Jim Lazarus said federal law prohibits local entities from creating benefit mandates.

In Sacramento, the Democratic-controlled Legislature sent Gov. Arnold Schwarzenegger a bill last week that would create a state-run universal health care system. He is expected to veto the bill.

For now, it's up to union and management negotiators to try to sort out who bears the burden.

In San Francisco, negotiators for 13 major hotels, in a two-year tussle with 4,300 workers represented by Unite Here Local 2, have proposed a two-tier system with a less-generous health care package for new hires.

New workers would face stiffer eligibility requirements and more- expensive co-payments. Those employees would have to work five years to be eligible for the level of coverage current workers have. Local 2 has rejected the proposal.

"It's indefensible," said Local 2 President Mike Casey, whose members recently voted to authorize a strike against the 13 hotels. "Why should a worker, by virtue of his or her hire date, who works just as hard performing the same duties, serving the same guests, have a lower standard than his or her co-workers? It creates instability in the workforce, turnover and divides workers."

Joe McInerney, the president of the American Hotel and Lodging Association, said he does not know details of the employers' proposal in San Francisco. Speaking generally, he said, conflicts over health coverage can be traced to the 9.2 percent increase in the cost of employer-sponsored health insurance in the United States in 2005. In California, those insurance costs jumped 8.2 percent.

"It's money and it's significant," McInerney said. "It's more than room rates have been increased and more than inflation. It becomes a substantial cost no matter how you cut it, especially if you look at what earnings were when we were recovering from the economic downturn and the effects of Sept. 11."

McInerney added, "If you have employees who were with the organization for a considerable time, you try to take care of them at the same level. New employees -- you try to scale it so that the cost in the first few years is not detrimental to the company. You have commitment to long-term employees that you do not have for your new employees."

If there is good news, it's that the rate of increase of health insurance premiums declined for the second consecutive year in 2005. In 2004, insurance premiums rose 11.2 percent.

Two-tier health coverage proposals are not new. Employers proposed them during the economic downturn of the early 1980s. "It went away in (the) 1990s when things were better and now it's back," said Ruth Milkman, director of the Institute for Labor and Employment at UCLA.

A two-tier proposal was at the core of a bitter strike and lockout of 60,000 supermarket employees represented by the United Food and Commercial Workers in Southern California in 2003 and 2004. When it ended, with damage done to both sides, the union reluctantly agreed to a permanent two-tier contract that called for reduced compensation and health coverage for new employees.

Supermarkets have thin profit margins. The employers, including Safeway, Albertson's and Kroger, said that Wal-Mart and other competitors with low labor costs had created an environment in which they had no other option than to reduce their own costs.

The food workers union was able to avoid a permanent two-tier system in Northern California contract negotiations covering about 20,000 workers without a strike. Still, the union's contract provides for a longer progression for new employees to reach the top tier of wages and benefits.

The contracts for 120,000 California supermarket clerks expire in 2007. Richard Benson, the president of the clerk's union Local 870 in Alameda County, expects that health care will again be the centerpiece of negotiations.

Meanwhile, the union and Safeway are jointly exploring ways to keep a lid on costs, in part by "keeping people healthy through various disease-management programs and proactive ways of addressing health care," Benson said.

Dan Rizzi, a labor law specialist at Nixon Peabody in Long Island, said employers must lead the way in creating programs that promote wellness, reward healthy employees and focus on the prevention and early treatment of serious illness.

"It is all about trying to create an environment where people are either healthy or where the conditions they have can be treated in an effective manner, thereby reducing costs down the road," Rizzi said.

He said his firm routinely sends e-mails reminding employees of the benefits of running, exercise and stress reduction.